# 43.Multiply-Strings

## 题目地址

https://leetcode.com/problems/multiply-strings/

## 题目描述

``````Given two non-negative integers num1 and num2 represented as strings, return the product of num1 and num2, also represented as a string.

Example 1:
Input: num1 = "2", num2 = "3"
Output: "6"

Example 2:
Input: num1 = "123", num2 = "456"
Output: "56088"

Note:
1. The length of both num1 and num2 is < 110.
2. Both num1 and num2 contain only digits 0-9.
3. Both num1 and num2 do not contain any leading zero, except the number 0 itself.
4. You must not use any built-in BigInteger library or convert the inputs to integer directly.``````

## 代码

### Approach #1 Two For-loop

``````class Solution {
public String multiply(String num1, String num2) {
int len1 = num1.length();
int len2 = num2.length();
if (len1 == 0 || len2 == 0)        return "0";

int result[] = new int[len1 + len2];

int i_n1 = 0;
int i_n2 = 0;

for (int i = len1 - 1; i >= 0; i--) {
int carry = 0;
int n1 = num1.charAt(i) - '0';

i_n2 = 0;
for (int j = len2 - 1; j >= 0; j--) {
int n2 = num2.charAt(j) - '0';

int sum = n1 * n2 + result[i_n1 + i_n2] + carry;

carry = sum / 10;
result[i_n1 + i_n2] = sum % 10;
i_n2++;
}

if (carry > 0) {
result[i_n1 + i_n2] += carry;
}

i_n1++;
}

int i = result.length - 1;
while (i >= 0 && result[i] == 0) {
i--;
}

if (i == -1) return "0";

String s = "";
while (i >= 0) {
s += (result[i--]);
}

return s;
}
}``````

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